1. Field of the Invention
This invention relates to a method of manufacturing a wear resistant sliding member especially useful for manufacturing a rotor housing for a rotary piston engine and the like.
2. Description of the Prior Art
The inner surface of a rotor housing in a rotary piston engine on which an apex seal on the rotor slides at high speed must be hard and highly wear resistant. It has been known to form a hard chromium plating layer on the inner surface of the rotor housing by plating the inner surface of the rotor housing with chromium and processing the plated chromium with reverse current as disclosed in U.S. Pat. No. 4,056,339. However, there is a great demand for rotor housing exhibiting much higher wear resistance capable of withstanding even higher speed and higher output of the engine.
The applicant found that a highly wear resistant rotor housing can be obtained by forming a hard chromium plating on the inner surface of the rotor housing, processing the hard chromium plating with reverse current to make it porous and forming a hard ceramic film on the hard chromium plating by vapor phase plating such as ion plating or sputtering. By virtue of the fact that the hard ceramic film is very hard and of the oil retaining effect of the surface pores, the rotor housing exhibits a superior wear resistance.
However, further investigation by the applicant has revealed that use of reverse current processing as the method for making the hard chromium plating layer porous is disadvantageous in that uniformly distributed pores cannot be obtained and the pores are V-shaped in cross section. The V-shaped pores are small in volume and the volume is significantly reduced as the surface of the rotor housing is worn. Accordingly the oil retaining amount is small and seizing can occur due to shortage of oil especially in parts where the pore density is low.